Method of manufacturing an electric lamp filament having a coiled-coil body portion with oriented off-set legs

ABSTRACT

A coiled-coil filament of refractory metal wire having longitudinally depending legs at each end that are joined to the coil barrel by open primary turns which are permanently bent through predetermined angles. The filament is initially wound as a continuous coil and, after the second coiling operation has been completed and the primary and secondary mandrels have been removed, selected primary turns in each of the then transversely extending legs are bent around an abutting stationary anvil to reposition the legs in the desired off-set relationship with the coil barrel.

United States Patent [151 3,670,377 Michael 1 51 June 20, 1972 1541METHOD OF MANUFACTURING AN [5 1 R n s u d ELECTRIC LAMP FILAMENT HAVINGUNITED STATES PATENTS A COILED'COIL BODY PORTION WITH 2,359,302 10/1944Curtis ..29/25.15 ORIENTED OFF-SET LEGS 2,723,926 11/1955 Bellott140/715 2,759,498 8/1956 Mann et a]... 140/71.5 [72] Invent lambparamus' v 3,048,201 8/1962 Johnson 140/715 73 Assignee; Westinghouse mCorporation, p 3,285,293 11/1966 Matheson 140/71.5

sburgh, Pa. Primary Examiner-John F. Campbell [22] F1led: May 12, 1970Assistant Examiner-Richard Bernard Lazarus 1 pp No 36 601 AnorneyA. T.Stratton, W. D. Palmer and D. S. Buleza [57] ABSTRACT A coiled-coilfilament of refractory metal wire having longitudinally depending legsat each end that are joined to the coil Related us'Applicafion Databarrel by open primary turns which are permanently bent Division f Ser.No June Pat No. through predetermined angles. The filament 1S wound 3588 579 as a continuous coil and, after the second coiling operation hasbeen completed'and the primary and secondary mandrels have been removed,selected primary turns in each of the then [52] U.S.Cl ..29/25.l8,-140/'7l..5 transversely extending legs are bent around an abutting [51 Int.Cl. ....H0lj 9/16, H01] 9/44 ntionary anvil to reposition the |egs inthe desired offlset re]a [58] Field of Search ..29/25.1, 25.11, 25.14,25. 15,11"

7 tionship with the coil barrel. 1

3 Claims, 7 Drawing figures PATENTEDJURZO m2 3. 670,377

w LL; WUHLM INVENTOR Jacob F Michael AGEN CROSS-REFERENCE TO RELATEDAPPLICATION This application is a division of application Ser. No.648,430 filed June 23, 1967 (now US. Pat. No. 3,588,579).

BACKGROUND OF THE INVENTION 1. Field of the Invention This inventionrelates to electric lamps and has particular reference to an improvedmethod for manufacturing coiledcoil filaments for incandescentprojection lamps and other light sources. I

2. Description of the Prior Art Certain types of projection lamps nowbeing marketed require low voltage so-called CC6 filaments. Thesefilaments comprise a refractory wire (viz., tungsten) helix having acoiled-coil body portion or barrel with longitudinally extending legs ateach end. The legs are attached to the lead-in conductors of the mountstructure and hold the filament in horizontal position within the lampenvelope in front of an internal reflector. Heretofore it has been thestandard practice v to wind a primary turn in the middle of each of thelegs at a juncture's thereof with the lead wires without an excessiveheat drain on the end turns of the coil barrel. These open turns orbreaks also served as a reference point for positively locating the endsof the tungsten or molybdenum inserts employed to short out and cool theleg ends. Such positive location of the leg inserts is required toproperly control the rating of the filament. A projection lamp having afilament with these features is disclosed in U.S. Pat. No. 3,383,539issued May 14, 1968 to R. F. Scoledge et al.

However, since the aforesaid open turns in the primary winding areformed before the second coiling operation and must be accuratelypositioned in the legs of the coil after the secondary coiling operationhas been completed, the latter operation had to be performed on manuallyoperated equipment. Such special primary coiling and hand-woundsecondary coiling are not only critical time-consuming operations butincrease the manufacturing cost of the filaments and make it difficultto control the filament rating.

SUMMARY OF THE INVENTION It is accordingly the general object of thepresent invention to provide a method for manufacturing such coiled-coilfilaments efficiently on a mass production basis using automatic primaryand secondary coiling machines of conventional design.

The foregoing objective and other advantages are achieved in-accordancewith the present invention by forming embryonic coiled-coil filaments oncontinuous primary-winding and automatic retractable-mandrelsecondary-winding machines known and used in the industry. The resultingcoils are then placed in a jig and a preselected turn in each of thetransversely extending legs is bent by suitable tools, such as a pair ofbending knives and an anvil, through a predetermined angle to form thedesired open turn or break in the legs and reposition the legs inlongitudinally extending and precise offset relationship with the coilbarrel.

BRIEF DESCRIPTION OF THE DRAWING A better understanding of the inventionwill be obtained by referring to the accompanying drawing, wherein;

FIGS. 1 and 2 are front and side elevational views, respectively, of anincandescent projection lamp containing the improved coiled-coilfilament of the present invention, portions of the envelope beingremoved to show the construction details of the filament and mountassembly;

FIG. 3 is an enlarged plan view of the filament and associated lead-inconductor portions of the mount along the line III-III of FIG. 1;

FIG. 4 is a similar view of a prior art filament and mount assembly; and

FIGS. 5 to 7 are enlarged elevational views of one end of the filamentshowing various phases in the leg-bending operation.

DESCRIPTION OF THE PREFERRED EMBODIMENT In FIGS. 1 and 2 there is showna 150 watt 21 volt T12 projection lamp 10 having a tubular vitreousenvelope 12 that has a domed top coated with a layer 13 of suitableopaque materia1 and which contains an elliptical reflector l4 and theimproved coiled-coil filament 16 of the present invention. The filament16 is supported in a substantially horizontal position at the focalpoint of the reflector 14 by a pair of rigid leading conductors 22 thatextend through a ceramic insulator 24 fitted into an opening in thereflector 14. As shown more particularly in FIG.'2, these conductors 22are spot welded to upstanding support wires 26 which are, in turn,fastened to a pair of rigid pins 28 hermetically sealed through avitreous disc or wafer 30 that is fused to and closes the mouth of theenvelope 12. A pair of auxiliary support wires 32 fastened to tabsprovided at the lower edge of the reflector l4 and to a pair of dummypins 34 hermetically sealed through the wafer 30 securely anchor thereflector in place. A cylindrical metal base 36 having a keyed centerpost 38 is cemented to the sealed end of the envelope 12 in accordancewith standard lamp-making practice.

As will be noted in FIGS. 1 and 2, the filament 16 has a coiled-coilbody portion or barrel that consists of a plurality of secondary turns17 and is terminated at each end by singly coiled straight leg portions18 that extend in the direction of the axis of the coil barrel and areattached to the conductors 22. As viewed in FIGS. 1 and 2, the filamentlegs 18 are both disposed in a plane that is substantially tangent tothe uppermost sides of the secondary turns 17 or top surface of the coilbarrel. When viewed in a direction normal to this plane, as depicted inFIG. 3, the aforesaid legs 18 are disposed in two separate plans'thatare parallel to and spaced predetermined distances from the proximatesides of the coil barrel. The filament 16 is thus held in predeterminedposition relative to the reflector 14 by the offset legs 18 and lead-inconductors 22 to which they are welded.

As shown most clearly in FIG. 3, the legs 18 are joined to therespective end (or terminal) secondary turns 17 by bent opened primaryturns 19 that are located predetermined and equal distances beyond theproximate sides of the coiled-coil. An insert 20 of molybdenum ortungsten is inserted into each of the legs 18 in accordance withstandard practice to facilitate welding the legs to the conductors 22and to cool them when the'filament 16 is energized. These inserts areseated against the bent primary turns 19 which thus serve as stops. Aswill also be noted, the primary turns that define the offset legportions 18 are of the same diameter and have the same spacing as theprimary turns in the coiled-coil body portron.

' turns 43 to straight outer leg sections 44. The inserts 20a arelocated within these outer leg sections 44, and the latter are welded tothe leads 22a.

FILAMENT MANUFACTURE AND LEG-BENDING OPERATION The coiled-coil filament16 is manufactured in accordance with the present invention by winding afine tungsten wire around a mandrel of dissimilar metal, such asmolybdenum, on a conventional automatic primary-coiling machine toprovide a composite wire having a continuous winding of uniformly spacedprimary turns. This composite wire is then automatically wound about asecond and larger mandrel on a conventional secondary-winding machinewhich has a mechanically retractable mandrel. The transversely extendinglegs of the resulting helix are automatically cut on the secondarymachine so that, after the primary mandrel has been chemically dissolvedin the usual manner, a leg 18 of predetermined length is left at eachend of the coil 16, as shown in FIG. 5.

The partly fabricated coils 16 are then placed in a jig which has apointed stationary anvil 46 that engages the outer surface of apreselected primary turn 19. The jig includes a pair of bending knives47 and 48 which, when actuated by a suitable known mechanism (notshown), are inserted between the primary turn 19 and the adjacentprimary turns from the opposite side of the leg 18. In the embodimenthere shown, a positioning bar 50 attached to the knife 48 is seatedagainst the proximate side of the coil barrel. Thus, a line tangent tothe secondary turns 17 is used as a reference surface for gaugingpurposes and insures that same primary turn 19 (the third turn beyondthe barrel in the case here illustrated) will be engaged by the anvil 46and knives 47, 48. This, in turn, controls the total number of primaryturns in the coil barrel and insures that the number of such turns ineach filament is the same, within a tolerance of plus or minus oneprimary turn. The filaments are thus reproducible and have the samerating.

When the anvil 46 and knives 47 and 48 are properly positioned, theknives are again actuated and swung in opposite directions through anangle of approximately 90, as shown in FIG. 6, around the stationarypivot point established by the anvil 46. The primary turn 19 is thusbent from its "as-wound configuration through an angle such that theportion of the embryonic leg 18 beyond the bent turn is disposed in thedesired parallel relationship with the axis of the coiled-coil. Thebending operation is repeated at the other end of the coil and the coilis removed from the jig. As is shown in FIG. 7, the finished coils 16thus have a sharply offset leg 18 at each end that is joined to the coilbarrel by a transversely bent and opened turn 19 which is spaced apredetermined and constant distance x beyond the barrel. The inserts 20are then placed in the legs 18 and the filament 16 is ready formounting.

As will be apparent from the foregoing, the object of the invention hasbeen achieved in that an efiicient method for making coiled-coil lampfilaments on a mass-production basis making coiled-coil lamp filamentson a mass-production basis has been provided. Experience has shown thatthe elimination of the discontinuous primary winding and the manualsecondary coiling operations effected by the present invention hasreduced the manufacturing cost of 2l volt CC6 filaments by approximately65 percent without any adverse effect on the coil quality.

While a preferred embodiment has been disclosed, it is to be understoodthat various modifications can be made without departing from the spiritand scope of the invention.

I claim as my invention:

1. The method of manufacturing an electric lamp filament having acoiled-coil body portion and angularly off-set legs, which methodcomprises;

winding a refractory metal wire around a first mandrel of dissimilarmetal to form a composite wire that includes a continuous primarywinding of wire,

winding a said composite wire around a second and larger mandrel andforming an elongated helix having a protruding leg portion ofpredetermined length at each end that extends transversely of thelongitudinal axis of said helix,

removing said first and second mandrels from said helix and therebyproducing a filament of refractory metal wire having a coiled-coiledbody portion with transversely depending legs at each end consisting ofa plurality of continuously wound primary turns, and

then bending only one selected primary turn of each of said legs in adirection and through an angle such that said selected primary turn ofeach leg is permanently deformed and opened and the portions of each ofthese legs beyond the respective selected bent primary turns extendlongitudinally with respect to the coiled-coil body portion of thefilament and are disposed in predetermined spatial relationship withrespect to one another and are offset relative to the coiled-coil bodyportion of the filament.

2. The method set forth in claim 1 wherein the bending of said selectedprimary turns is achieved by applying deforming pressure to portions ofsaid selected primary turns that are located on either side of astationary pivot point that is established at an outwardly disposedsurface of the respective turns.

3, The method set forth in claim 2 wherein;

said first mandrel is removed by chemical dissolution,

said second mandrel is mechanically withdrawn from the composite wirehelix, and

the selected primary turns to be bent are located by contacting the sideof the coiled-coil body portion of the filament and utilizing it as areference surface for the turn-bending means.

1. The method of manufacturing an electric lamp filament having acoiled-coil body portion and angularly off-set legs, which methodcomprises; winding a refractory metal wire around a first mandrel ofdissimilar metal to form a composite wire that includes a continuousprimary winding of wire, winding a said composite wire around a secondand larger mandrel and forming an elongated helix having a protrudingleg portion of predetermined length at each end that extendstransversely of the longitudinal axis of said helix, removing said firstand second mandrels from said helix and thereby producing a filament ofrefractory metal wire having a coiled-coiled body portion withtransversely depending legs at each end consisting of a plurality ofcontinuously wound primary turns, and then bending only one selectedprimary turn of each of said legs in a direction and through an anglesuch that said selected primary turn of each leg is permanently deformedand opened and the portions of each of these legs beyond the respectiveselected bent primary turns extend longitudinally with respect to thecoiled-coil body portion of the filament and are disposed inpredetermined spatial relationship with respect to one another and areoffset relative to the coiled-coil body portion of the filament.
 2. Themethod set forth in claim 1 wherein the bending of said selected primaryturns is achieved by applying deforming pressure to portions of saidselected primary turns that are located on either side of a stationarypivot point that is established at an outwardly disposed surface of therespective turns.
 3. The method set forth in claim 2 wherein; said firstmandrel is removed by chemical dissolution, said second mandrel ismechanically withdrawn from the composite wire helix, and the selectedprimary turns to be bent are located by contacting the side of thecoiled-coil body portion of the filament and utilizing it as a referencesurface for the turn-bending means.